Energy absorber and evaporative cooling system

ABSTRACT

A transmission line termination load or attenuator device is provided with energy absorbing means including a medium for absorption of thermal energy, particularly, in the electromagnetic spectrum. The device is coupled to an evaporative type cooling system to evolve a relatively low pressure, low flow rate means for handling extremely high power levels with a relatively small volume of absorbent. The device utilized in either application has substantially low reflection coefficient characteristics over relatively wide frequency bandwidths and may be in either rectangular or coaxial waveguide configurations.

O United States Patent 1151 3,660,784 Schar fman 1 May 2, 1972 1 ENERGYABSORBER AND FOREIGN PATENTS OR APPLICATIONS EVAPORATIVE COOLING SYSTEMl,l38,865 2/1957 France .333/22 [72] Inventor: Howard Scharfman,Lexington, Mass. OTHER PUBLICATIONS [73] Assignee: Raytheon CompanyLexingwn Mass Bogart Bulletin Vol. I No. 3 January 1961 Pulisher-Bulletin, 221 Filed: Aug. 28, 1970 Brooklyn, 6 p

[ PP 67,723 Primary E.\'aminerHerman Karl Saalbach AssistantExaminer-Marvin Nussbaum 52 us. c1 .333 22 F, 333/81 A, 333/81 B, g""i-" Murphy JsePh Panmne and Edga' 333/98 R OS [51] Int. Cl ..Hlp 1/22,HOlp 1/26 57 CT [58} Field ofSeai-ch ..333/22, 81; 62/DlG. 12

A transmission line termination load or attenuator device is 56]References Cited provided with energy absorbing means including a mediumfor absorption of thermal energy, pamcularly, in the electromag- UNITEDSTATES PATENTS netic spectrum. The device is coupled to an evaporativetype cooling system to evolve a relatively low pressure, low flow2,262,134 11/1941 Brown ..333/22 rate means for handling extremely powerlevels i a 2722'616 11/1955 Mosesrelatively small volume of absorbent.The device utilized in 3241'089 3/1966 333/22 either application hassubstantially low reflection coefficient 2,850,702 9/ l 95 8 White....333/22 characteristics over relatively wide frequency bandwidths and2,434,560 l/l948 Gunter ...333/22 may be in either rectangular or i lwaveguide configure tions.

Claims, 6 Drawing Figures cor/05115155 2 28 4 2/ LOSSY ELECTRICAL I 24,0 g 6 cououcron 32 g.-

RF /6 a 38 I l l I i QLggLIARY /7 LANT :kfl 3 SOURCE .11 g 22PATENTEDMAY 21972 SHEET 10F 2 ONDENSER LOSSY ELECTRICAL CONDUCTORAUXILIARY COOLANT SOURCE I I J F/GI 2 m M 4 42 A TH ERMALLY CON DUCTIVEPARTICLES THERMALLY CONDUCTIVE 4 PARTICLES FLUID COOLANT F 2 FLUIDCOOLANT PATENTEDMAY 21912 3, 660.784

sum 2 OF 2 MICROWAVE ENERGY ABSORBING MATERIAL ELECTRICAL AND THERMALCONDUCTIVITY MICROWAVE ENERGY THERMALLY PERMEABLE CONDUCTIVE FLUID e000THERMAL 60 PARTICLES COOLANT V CONDUCTIVITY LovyglE-LEcTRlc L76 4 LossMICROWAVE ZIEJLSIPANT ENERGY F/@ 5 ABSORBING MATERIALS FLUID COOLANTENERGY ABSORBER AND EVAPORATIVE COOLING SYSTEM BACKGROUND OF THEINVENTION 1. Field of the Invention The invention relates toelectromagnetic energy termination and attenuator devices.

2. Description of the Prior Art In the prior art the termination oftransmission lines, as well as attenuation of energy at intermittentpoints, particularly, at high power levels, presents a continuingproblem in view of the thermal absorption and dissipation requirements.Additionally, it is necessary to match impedances over substantiallybroad frequency ranges to provide reflectionless electricalcharacteristics. Prior art devices have evolved having lengths which mayrun into many feet, at for example, radio frequencies, and combined withthe weight of the absorbing materials, such loads have becomeobjectionably bulky and expensive. The high temperatures generated,particularly, with the bulky dry load materials, have also createdproblems in achieving the desired electrical characteristics of energytransmission systems. Further, such termination devices for use inwaveguide, as well as in coaxial transmission lines, have been commonlyprovided with rather lengthy tapered structures to provide for impedancematching. Such lengthy structures may be disadvantageous when systemsare operated under conditions of shock and vibration.

Attenuators for high frequency energy transmission systems are alsoquite elaborate involving numerous components such as sidewall couplersand phase shifters consuming many square feet of area along withattendant cost and weight problems. The combination of the numerousprior art components in such attenuator structures has also resulted inintolerably high insertion loss values over the frequency bands ofinterest. In addition, attenuator devices heretofore employed in highpower systems are extremely frequency sensitive and hence, unsuitablefor broadband frequency applications.

Ideally, energy absorbing termination loads, as well as attenuators,must be capable of handling output power levels which can be as high asmany hundreds or thousands of watts of average power, as well asmegawatts of peak power, with substantially no reflection of energy andwith VSWR ratings, desirably between 1.01 and 1.5. Improved termination,as well as attenuation devices, therefore, of minimal mechanicalconfiguration and reduced insertion loss characteristics over relativelybroad frequency bands are essential for more effective utilization, forexample, of microwave energy systems.

SUMMARY OF THE INVENTION In accordance with the teachings of the presentinvention a transmission line attenuator or termination device isprovided with a lossy dielectric absorbing medium extending along a pathangulated to the path of the energy. In applications where the device isutilized as a microwave frequency attenuator a section of waveguide isflanged at opposing ends. In the applications for termination oftransmission lines an energy absorber is housed within a waveguidesection having a flange at only one end.

In one illustrative embodiment a tubular member of a substantially lossyelectrical conductivity is filled with particles having a high thermalconductivity and the absorber is angularly disposed within a section ofhollow pipe transmission line. As the electromagnetic energy is absorbedby the lossy conductor, the resultant heat is rapidly dissipated by theprocess of thermal conduction along the tube, as well as throughout theparticles of thermally conductive material housed therein. A fluiddielectric coolant such as water or oil is directed through the tubularmember by means of a closed loop evaporative cooling system at arelatively low flow rate and pressure. The fluid coolant circulating inthe system is rapidly vaporized by the absorbed thermal energy. Theresultant vapor is condensed and traverses a heat exchanger mechanismutilizing an auxiliary coolant such as the '-local domestic watersupply. The condensed and cooled'fluid medium is filtered and may berecirculated to the energy absorber means or discharged.

Numerous alternative embodiments involving a combination of conductiveand lossy energy absorbing materials are disclosed, as well asstructures with or without thermally conductive particles dependent onthe energy levels to'be handled. In all cases the absorbed energy ispermitted to heat the contacted surfaces to a temperature in excess ofthe fluid boiling point to vaporize such fluids circulating through thesystem and thereby transport exceedingly high thermal energy levels. Anoutstanding feature of the invention is the capability of absorbingexceedingly high electromagnetic energy including infrared and microwavefrequencies utilizing a relatively small volume of the absorbentmaterial. Impedance matching means such as suitable transitions, tapers,steps, stubs, and other matching devices will yield a device capable ofachieving the low reflection coefficient characteristics over broadfrequency bands.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the detailsfor the provision of illustrative embodiments, will be readilyunderstood after consideration of the following detailed description andreference to the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of the energy absorber together with aschematic representation of a coupled evaporative cooling system;

FIG. 2 is partial cross-sectional view of an alternative embodiment ofthe energy absorber;

FIG. 3 is a partial cross-sectional view of another alternativeembodiment of the energy absorber;

FIG. 4 is a partial cross-sectional view of still another alternativeembodiment of the energy absorber;

FIG. 5 is a partial cross-sectional view of another alternativeembodiment of the invention; and

FIG. 6 is a cross-sectional view of an attenuator embodying thestructure of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the FIG. 1 acomplete device 2 for microwave frequency energy absorption and thermaldissipation is shown for termination load applications. Such structureis generally found in an arrangement with the termination device mountedin an auxiliary transmission line which is coupled to the maintransmission line of a radar system by means of a coupling aperture in aside or common wall. The terminal load devices are also employed inmultiported directional coupler transmission line arrangements. Thedisclosed structure is used for absorbing the incident microwave energy,as well as measuring transmitted power by any of the well knowncalorimetric techniques utilizing the temperature differential ofcirculating fluid coolants.

A section of hollow pipe transmission line 6 of either rectangular orcoaxial waveguide is enclosed at one end by a terminal conductive endwall 8 which may be fixed or movable in the well known manner, aspreferred, for tuning purposes over the frequency bands of interest. Theopposing end of waveguide section 6 supports a mounting flange member 10for coupling the device to adjacent waveguide transmission lines bysecuring means introduced through coupling apertures 12. The flangemembers may have conventional choke arrangements and are selected alongwith the waveguide section in accordance with the standard microwave artfor the propagation of electromagnetic energy at a particular range offrequencies of operation. Suitable transformation structures are coupledto the terminal load or incorporated therein such as steps, stubs, orother matching techniques to provide for a low reflection coefficient ofthe propagated energy. Such impedance matching structures are well knownin the art and have not been enumerated or described herein for the sakeof clarity. Further, while the flanged waveguide section has been shownfor illustrative purposes, the device of the invention may be mounted inany transmission line arrangement by being incorporated directly in adirectional coupler or any conjugate hybrid junction coupler.

The microwave energy absorber 14 in this embodiment comprises a tubularconductor 16 of lossy electrical conductive properties at theelectromagnetic wave frequencies of interest, for example, 300megacycles per second and higher. A dielectric fluid medium 18, such aswater or oil, is circulated through conductor 16 at relatively lowpressure and flow rates. The absorbed incident microwave energy rapidlyheats the conductor until temperatures well in excess of the fluidboiling temperatures are attained. The coolant traversing the walls ofconductor 16 reaches its heat evaporization value to become steam asdepicted by numeral 20 to transport and dissipate the high thermalenergy derived from the microwave power. The ends of conductor 16 areprovided with fluid retaining members 22 and 24 to define, respectively,inlet port 26 and outlet port 28 coupled to an evaporative coolingsystem 4. The energy absorbing element 14 is supported by tubularmembers 30 and 32 joined to the broad walls of, for example, arectangular waveguide section 6. It is noted that the absorbing element14 is inserted within the waveguide section at an inclined angle to itscenter line to assist in achieving broadband low reflection coefficientelectrical characteristics.

The vaporized fluid coolant exits through port 28 and is coupled to acondenser arrangement 34 where the vapor is transformed again into aliquid. A heat exchanger 36 is incorporated in the evaporative system toeffectively cool the transformed condensed fluid and lower the thetemperature of same through a combination of convection and conductionutilizing an auxiliary coolant source 38 such as, for example, the citywater supply. An excellent example of an efficient and compact heatexchanger structure is disclosed in copending application for U.S.Letters Patent, Ser. No. 10,334, filed Feb. I l, 1970, by William H.Hapgood and assigned to the assignee of the present invention. Inaccordance with this application a heat transfer structure and system isdisclosed including a matrix of tubes and spheres bonded together toprovide a conduit for a first fluid and a plurality of interconnectedpaths for a second fluid. The paths are made up of the spaces betweenthe spheres such that the walls of the paths are portions of sphericalsurfaces. The total path length is made less than 20 times the averageradius of curvature of the spherical surfaces and the spacing betweenadjacent tube elements is of the same order of magnitude as the averagelength of the paths. A heat exchanger so constructed will effectivelytransfer substantially all the heat in a heated fluid in average pathlengths of 1 inch or less. The fluid medium in the closed loop system iscirculated by means of a relatively low pressure pump 40. The condensedcooled fluid may also be filtered by any conventional means 42 and isfed back to the microwave energy absorber through inlet port 26. Theutilization of relatively low fluid rates, as well as low circulatingpressures, simplifies and reduces the cost of the evaporative coolingsystem in relation to such components as the ports, valves, joints, andseals. Such pressures also improve the reliability of the system.

Referring now to FIG. 2, an alternative microwave energy absorber isillustrated. A tubular conductor 44 is fabricated of a material havingsimilar lossy electrical characteristics as conductor 16. An exemplarymetal such as tungsten, nickel, or nichrome which is substantially lossyat the microwave operating frequencies may be employed. The hollowpassageway 46 is substantially filled with particles, such as shavings,spheres, ovoids, cubes, or any other suitable heat exchangingconfiguration of a highly thermal conductive material such as copper,aluminum, stainless steel, or any of the conductive plastic materials tocollectively define a matrix structure 48. The fluid coolant willtraverse along the hollow passageway 46 and absorb the heat which isthermally conducted along the walls of the conductor 44, as well as theparticles 48 contained inside the absorber. The relatively hightemperatures envisaged by the absorption of the microwave power incidentupon the walls of the tubular conductor 44, are in excess of the boilingpoint of the fluid coolant and thereby vaporize such coolant before itexits through outlet port 28. The vaporized coolant is coupled to theevaporative cooling system similar to the arrangement discussed inreference to FIG. 1.

Referring now to FIG. 3, another alternative embodiment of the microwaveenergy absorber is illustrated. In this embodiment a tubular conductor50 is coated throughout its inner surfaces by thermally bonded finethermally conductive particles to define a wall surface 52. Thecirculating fluid coolant contacting the wall surfaces 52 will berapidly vaporized as it passes through the passageway by reason of thethermal conduction from the outer wall surface 50 of the tubularconductor. The appropriate selection of materials for conductor 50, aswell as the bonded and impregnated particles are selected for thedesired power levels to provide the appropriate thermal conductioncharacteristics to achieve the heat of vaporization level of thecirculating coolant. I

Referring next to FIG. 4, still another alternative embodiment of theinvention is shown for the tubular conductor of the microwave absorbingelement. A high electrically, as well as thermally conductive materialsuch as copper or aluminum is utilized for the main tubular body 54. Theouter wall surfaces are coated by any suitable techniques such asplating, diffusion or wrapping with a material having a high loss at themicrowave frequencies under consideration to provide a contactingsurface layer 56. One suggested material to be utilized for the outerenergy absorbing medium would be a pyrolytically deposited coating ofgraphite.

In FIG. 5, still another alternative embodiment is shown. A tubularmember 58 is selected from a low loss energy permeable material havingfair to good thermal conductivity. Some illustrative materials includeglass, ceramic, as well as plastic. Within the conductor member 58 apacking of thermally conductive particles 60 substantially enclose theinternal passageway. The fluid coolant will dissipate the microwaveenergy absorbed through thermal conduction by passing through the matrixof particles and subsequently vaporize such fluid. Alternatively, thepacking matrix 60 may comprise particles of a low loss dielectric havinga fair to good thermal conductivity. In either embodiment theappropriate flow rate, as well as fluid coolant is selected to optimizethe transporting of the absorbed microwave energy by the vaporizedcoolant.

- FIG. 6 illustrates the attenuator application where the amplitude of awave in a transmission system is controlled with a minimum ofdistortion. In such applications a waveguide section 62 has securedadjacent opposing ends mounting flanges 64 and 66. In this example, asin the previous embodiments, the microwave absorbing element 68 isdisposed angularly with respect to the direction of the propagatedwaves. The fluid medium 70 contacting the walls of conductor 72 absorbsheat by thermal conduction to vaporize the fluid. An evaporative coolingsystem is coupled to each end of the tubular conductor. The parameterssuch as flow. rates and materials may be selected to provide the degreeof attenuation desired.

There is thus disclosed an efficient electromagnetic energy absorbingmeans and associated cooling system for handling very high power levels.In those applications where the handling of lower energy levels iscontemplated, suitable adjustment such as the omission of packingmaterials having the high thermal conductivity characteristics in theabsorbing means may be practiced similar to the device illustrated inFIG. 1. Many heat dissipation means for the condensed fluid may also beemployed within the teachings of the invention. Numerous modifications,alternations and variations, therefore, in structure, as well as theselection of the energy absorbing materials, will readily occur to thoseskilled in the art without departing from the spirit and scope of theinvention as defined in the appended claims. It is intended that theembodiments shown and described herein be considered as illustrativeonly and not in a limiting sense.

What is claimed is:

1. In combination: I

a source of electromagnetic energy;

means for absorbing said energy comprising a hollow member of a lossyelectrically conductive material containing a plurality of thermallyconductive members;

and means for dissipating the absorbed energy including an evaporativefluid cooling system coupled to said energy absorbing means.

2. An electromagnetic energy attenuator device comprising:

means for propagating said energy along a path;

means for absorbing said energy disposed in said path including a hollowmember of a lossy electrically conduc tive material and a fluid coolantflowing therethrough;

said hollow member containing a plurality of thermally conductivemembers for vaporizing the fluid coolant to dissipate absorbed heat;

and an evaporative cooling system coupled to said energyabsorbing means.

3. An electromagnetic energy termination device comprismeans forpropagating said energy along a path;

means for tenninating said path in an energy reflecting end member;

means for circulating a fluid coolant;

means for absorbing electromagnetic energy including a hollow member ofa lossy electrically conductive material containing a plurality ofthermally conductive members for converting the absorbed energy bythermal conduction to a level sufficient to vaporize said fluid coolant;

and a closed loop evaporative cooling system coupled to said energyabsorbing means.

4. In combination:

a source of electromagnetic energy;

means for absorbing said energy comprising a hollow member having aninner wall surface of a high thermal conductivity material;

and means for dissipating the absorbed energy including an evaporativefluid cooling system coupled to said energy absorbing means.

5. In combination:

a source of electromagnetic energy;

means for absorbing said energy comprising a hollow member of an energypermeable material containing a plurality of thermally conductivemembers;

and means for dissipating the absorbed energy including an evaporativefluid cooling system coupled to said energy absorbing means.

1. In combination: a source of electromagnetic energy; means forabsorbing said energy comprising a hollow member of a lossy electricallyconductive material containing a plurality of thermally conductivemembers; and means for dissipating the absorbed energy including anevaporative fluid cooling system coupled to said energy absorbing means.2. An electromagnetic energy attenuator device comprising: means forpropagating said energy along a path; means for absorbing said energydisposed in said path including a hollow member of a lossy electricallyconductive material and a fluid coolant flowing therethrough; saidhollow member containing a plurality of thermally conductive members forvaporizing the fluid coolant to dissipate absorbed heat; and anevaporative cooling system coupled to said energy-absorbing means.
 3. Anelectromagnetic energy termination device comprising; means forpropagating said energy along a path; means for terminating said path inan energy reflecting end member; means for circulating a fluid coolant;means for absorbing electromagnetic energy including a hollow member ofa lossy electrically conductive material containing a plurality ofthermally conductive members for converting the absorbed energy bythermal conduction to a level sufficient to vaporize said fluid coolant;and a closed loop evaporative cooling system coupled to said energyabsorbing means.
 4. In combination: a source of electromagnetic energy;means for absorbing said energy comprising a hollow member having aninner wall surface of a high thermal conductivity material; and meansfor dissipating the absorbed energy including an evaporative fluidcooling system coupled to said energy absorbing means.
 5. Incombination: a source of electromagnetic energy; means for absorbingsaid energy comprising a hollow member of an energy permeable materialcontaining a plurality of thermally conductive memberS; and means fordissipating the absorbed energy including an evaporative fluid coolingsystem coupled to said energy absorbing means.